S41936-019-0080-8.Pdf

Gosavi et al. The Journal of Basic and Applied Zoology (2019) 80:9 The Journal of Basic https://doi.org/10.1186/s41936-019-0080-8 and Applied Zoology

RESEARCH Open Access Assessing the sustainability of lepidophagous catfish, Pachypterus khavalchor (Kulkarni, 1952), from a tropical river Panchaganga, Maharashtra, India Sachin M. Gosavi1,2,3*† , Sanjay S. Kharat1†, Pradeep Kumkar1 and Sandip D. Tapkir1,4

Abstract Background: The Western Ghats of India, one of the global biodiversity hotspots and freshwater eco-regions, harbors several fish species which not just form the important part of the world’s freshwater biodiversity yet in addition are the vital segment of livelihood of the neighborhood population. The rate of fish decline in the Western Ghats is alarming. The absence of organized study and data scarcity on basic biology and life history traits of several species could be one reason behind the decline, and thus it is difficult to execute conservation action/s. This is especially true, particularly for data-deficient species for which definite data related to distribution, population size, and trend is not available. The present study deals with the detailed investigation of population dynamics of catfish species, Pachypterus khavalchor, which is data-deficient species inhabiting the Western Ghats of India and forms an important component of freshwater inland fishery, providing nutritional and financial security to the local community. Methods: Specimens for the present study were collected monthly for a period of 1 year from the River Panchaganga and length–frequency data were analyzed using FiSAT II software. Results: Length–weight analysis of pooled (male + female) data suggested the fish exhibited higher exponent than expected under isometry, indicating the positive allometric growth of P. khavalchor in the Panchaganga River. The asymptotic length (L∞)andthegrowthrate(K) were estimated as 149.63 mm and 0.71 year−1 respectively. Potential longevity (tmax) and length at first capture (Lc) were estimated as 4.22 years and 73 mm respectively. The total (Z), natural (M), and fishing mortality (F) were estimated as 2.23 year−1,0.88year−1,and −1 1.35 year respectively. The current exploitation rate (Ecur = 0.60) was found to be almost 90% that gives the maximum relative yield per recruit (Emax = 0.67). Recruitment pattern revealed two peaks, suggesting the fish have two spawning bouts each year. Conclusions: The stock of P. khavalchor in the Panchaganga River may be in near full exploitation under the current harvesting strategy, with a high chance of recruitment failure in the future. Additional studies on the reproductive biology of P. khavalchor would be particularly welcome for the imposition of the seasonal closure for effective conservation of stock. Keywords: Lepidophagy, Fishery, Data scarcity, Freshwater ecosystem, Recruitment, Aquatic conservation, Mortality

* Correspondence: [email protected] †Sachin M. Gosavi and Sanjay S. Kharat contributed equally to this work. 1Department of Zoology, Modern College of Arts, Science and Commerce, Ganeshkhind, Pune, Maharashtra 411 016, India 2Post Graduate Research Centre, Department of Zoology, Modern College of Arts, Science and Commerce, Shivajinagar, Pune, Maharashtra 411 005, India Full list of author information is available at the end of the article

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Background 2012; Eschmeyer et al., 2018). Each of these species is ex- The Western Ghats of India is well known for its exclusive tremely delicious and having good market demands in their biodiversity and also classified as a freshwater eco-region distribution range and thus provides dietary and financial with more than 300 species of the freshwater fishes (Abell advantage to the local community (Buragohain, 2018; et al., 2008;Molur,Smith,Daniel,&Darwall,2011;Myers, Gosavi,Kharat,Kumkar,&Navarange,2018;Kumbar& Mittermeier, Mittermeier, Da Fonseca, & Kent, 2000). Lad, 2014). Since Pachypterus species forms an important Nearly 30% of the species inhabiting the Western Ghats part of the open-access fisheries, they are getting exploited have been categorized as threatened in the IUCN Red list in their distribution range leading to a huge decline in (Dahanukar, 2011; Dahanukar, Raghavan, Ali, Abraham, & population (Buragohain, 2018;Kumbar&Lad,2014). In Shaji, 2011; , Ramprasanth, Ali, & Dahanukar, 2018a). support to this, Dahanukar (2011) and Menon (1999) However, several endemic and threatened species con- already pointed that several anthropogenic activities such tinue to be harvested at unsustainable levels through arti- as urbanization, industrial developments, and mining are sanal and open-access fisheries throughout the Western contributing to dwindling population of P. khavalchor. Ghats (Das et al., 2017; Keskar, Raghavan, Kumkar, Menon (2004)andMoluretal.(2011) further suggested Padhye, & Dahanukar, 2017; Kharat & Dahanukar, 2013; that it could be a threatened species due to its fragmented Prasad, Ali, Harikrishnan, & Raghavan, 2012; Raghavan, population and non-availability of population data. As a Ali, Dahanukar, & Rosser, 2011; Raghavan et al., 2018a). result, presently, P. khavalchor is categorized as the “data According to Darwall et al. (2018), another most import- deficient” species by IUCN (Dahanukar, 2011; Dahanukar ant and fundamental cause for the freshwater biodiversity et al., 2012;IUCN,2018). However, despite of the variety of crisis is the insufficient consideration of impacts on fresh- threats operating on the P. khavalchor presently, no conser- water ecosystems in decision-making and policy. However, vation action plans are specifically directed towards conser- decision-making and policy establishment require the reli- vation of this species. As a result of combined threats from able data on the population dynamics/trend, and thus the different sources, data deficiency, and suggested possibility information inadequacy on population dynamics for ma- of the loss of this freshwater catfish species by (Menon, jority of endemic species hindered the development of ap- 1999), it is an immediate need to generate the data on the propriate conservation action plans (Cooke, Paukert, & life history traits of P. khavalchor for instantaneous con- Hogan, 2012; Dahanukar et al., 2011; Luiz, Woods, Madin, servation action. &Madin,2016;Moraisetal.,2013). At present, the West- The persistence of any fish species in the given habitat ern Ghats of India harbor 26 data-deficient species and is dependent on the life history traits of that species majority of them are likely to be threatened with extinc- (Das et al., 2017, 2018; Kumar et al., 2014; Prasad et al., tion (Dahanukar et al., 2011; Molur et al., 2011). Because 2012; Raghavan et al., 2011, 2018a). Under the present of lack of substantial information on population dynamics, environmental conditions, life history traits must gener- the data-deficient species are not at the forefront of the ate sufficient recruitment for a given population to per- conservation agenda (Luiz et al., 2016;Moraisetal.,2013; sist. In this context, considerable knowledge on length– Possingham et al., 2002). As data deficiency not only means weight relationships, growth, population structure, mor- the absence of records, but it may indicate dangerously low tality (natural and fishing), exploitation level, and re- abundance, Mace et al. (2008) clearly stated that “data-defi- cruitment pattern of an exploited stock is essential for cient species should be afforded the same degree of protec- planning and management of fisheries resources, mainly tion as a threatened species until more information is when the species form the important component of the forthcoming.” Keeping the above thought in view, it is fun- artisanal fisheries and lies at the base of the higher food damentally critical to have data on population biology pa- web (Das et al., 2017, 2018; Kumar et al., 2014). There- rameters of known data-deficient species inhabiting the fore, present investigation was carried out for the assess- Western Ghats of India for their effective conservation and ment and evaluation of various life history traits of P. management. khavalchor using length–frequency data collected for The catfish genus Pachypterus consists of three species one year. This study generates first of its kind informa- viz. Pachypterus acutirostris (Day, 1870) distributed in tion on the life history traits and population dynamics of Irrawaddy, Sittang, and Bago rivers, Myanmar (Eschmeyer, the genus Pachypterus in general and P. khavalchor in Fricke, & van der Laan, 2018;Kottelat,2013); Pachypterus particular. atherinoides (Bloch, 1794) distributed in river drainages of the Indian subcontinent north of the Cauvery, Bangladesh, Methods Nepal, and Pakistan (Ahamed et al., 2018; Buragohain, Study area, fish collection, and measurements 2018; Eschmeyer et al., 2018); and Pachypterus khavalchor Monthly samples were collected during June 2015 to (Kulkarni, 1952) which inhabits the Krishna River basin of May 2016 with the help of a small-scale artisanal fisher- Peninsular India (Dahanukar, Paingankar, Raut, & Kharat, men from the Panchaganaga River (17.28 °N; 74.18 °E), Gosavi et al. The Journal of Basic and Applied Zoology (2019) 80:9 Page 3 of 10

Maharashtra, India. The fishing method employed in this fitting the classical von Bertalanffy growth function area by local fishermen mainly includes the use of gill net (VBGF) as: and cast net of variable mesh size. Specimens (n =427) ¼ ∞Ã ½ð À ð− ðÞ− ðÞ were collected and brought to the laboratory in ice-filled Lt L 1 Exp Kt to 2 ’ boxes. Standard length (SL; a fishs body length from the tip In Eq. 2, L∞ represents asymptotic length; K is the of its snout to end of its last vertebrae; it includes every- VBGF curvature parameter (growth constant), Lt is the thing except the caudal fin) and total length (TL; it is the length at time t, and t0 is the hypothetical length at the length of a fish from the tip of its snout to the end of the age length zero. Using growth parameters (L∞) and longer lobe of its caudal fin) were measured for each speci- VBGF curvature parameter (K), the Growth performance men to the nearest 0.01 mm using a digital vernier caliper index (Ø′) was calculated as (Pauly, 1979; Pauly & (Mitutoyo, Japan). Weight (W) was determined to the Munro, 1984): closest 0.01 g using digital weighing balance (Contech, 0 India). Specimens were fixed in 10% formalin after all mea- Ø ¼ LogK þ 2 logL1 ð3Þ surements and are in the departmental collection of Mod- ern College of Arts, Science and Commerce, Ganeshkhind, The potential longevity (tmax) was obtained using the Pune, Maharashtra, India. Growth, potential longevity, equation tmax =3/K, given by Pauly (1983). Maximum mortality, recruitment pattern, probability of capture, possible extreme length for this species was calculated length structured virtual population analysis (VPA), relative using the support function available in FiSAT II (Forma- yield per recruit, and biomass per recruit were estimated cion, Rongo, & Sambilay, 1991). A selectivity curve was using FAO–ICLARM Stock Assessment Tools II (FiSAT II, generated using linear regression fitted to the ascending version 1.2.2) software (Gayanilo Jr., Sparre, & Pauly, 1998). data points from the plot of probability of capture against length, which was used to estimate the final – Length weight relationships (LWRs) value of length-at-first capture (Lc or L50). LWR parameters were estimated according to the guidelines and equation given by Froese (2006): Mortality The length-converted catch curve was applied for the calculation of the total mortality (Z) (Pauly, 1983). W ¼ SLb ð1Þ a Natural mortality (M) was determined using the follow- ing Pauly’s empirical equation (Pauly, 1980), where W is the body weight (g), SL is the standard length (cm), “a” is the intercept, and “b” is the slope of ln ðÞ¼M −0:0152−0:279 ln ðÞL∞ log-transformed linear regression. The coefficient of de- þ 0:6543 ln ðÞþK 0:463 ln ðÞT ð4Þ termination (r2) was estimated as the goodness of fit. where T is the average annual temperature, which is Student’s t test was used to find out whether “b” value 26 °C. significantly deviated from the expected cube value of 3 Fishing mortality was (F) calculated by subtracting the (Sokal & Rohlf, 1987; Zar, 1984). The values of standard M value from the Z value (Appeldoorn, 1984): length and parameter b were compared with values in FishBase (Froese & Pauly, 2018). Analyses were per- F ¼ ðÞZ À M ð5Þ formed using the program PAST version 3.13 (Hammer, Harper, & Ryan, 2001). Values of F and Z were used to calculate the current exploitation rate (Ecur) as per the formula given by Population structure Gulland (1985): Frequency distribution forms the basis for the analysis, Ecur ¼ F=Z ð6Þ and thus standard length data were grouped in a length– frequency table with 2.5 mm as the smallest mid-length Whether the present fishery resource status of study and 5 mm class intervals thereafter. To determine the species is sustainable or not was assessed according to population structure, contour plot was plotted using 10 Etim, Lebo, and King (1999), where Z/K ratio ≈ 2 indi- mm length class of standard length (SL) in relation to dif- cate over-exploitation. ferent months. Exploitation Growth and potential longevity The growth and mortality parameters were used as input Asymptotic length (L∞) and the growth coefficient (K) for the length-structured virtual population analysis were estimated using ELEFAN 1 method (Pauly, 1981, (VPA) analysis (Hilborn & Walters, 1992). Further, the 1982; Pauly & David, 1981; Pauly & Morgan, 1987)by current level of exploitation (Ecur) was estimated using Gosavi et al. The Journal of Basic and Applied Zoology (2019) 80:9 Page 4 of 10

relative yield per recruit (Y′/R) and biomass by recruit 143.51 mm respectively. Total mortality (Z) and natural − (B′/R) analysis with the Knife–Edge selection method mortality coefficient (M) were found to be 2.23 year 1 −1 (Beverton & Holt, 1966). Values of E50 (i.e., exploitation and 0.88 year respectively. Fishing mortality coefficient − rate that resulted in a devalued of the unexploited bio- (F) was found to be 1.35 year 1. mass by 50%) and Emax (i.e. exploitation rate producing The virtual population analysis (Fig. 4) revealed high maximum yield) were calculated by plotting Y′/R vs. Ecur natural mortality at a young age though the fishery prin- and of B′/R vs. Ecur. cipally targeted comparatively large sized individuals (from 52.5 mm onwards) as evident by the exponential Probability of capture and recruitment pattern decrease in survival rate. Exploitation levels estimated The probability of capture was estimated using the using relative yield-per-recruit (Y′/R) and relative length-converted catch curve (Pauly, 1984). Recruitment biomass-per-recruit (B′/R) analysis based on knife edge pattern provides information related to the number of selection were found to be 0.36 (E50) and 0.67 (Emax) pulses per year and the relative strength of each pulse respectively (Fig. 5; Table 2). The current level of ex- and therefore was calculated by reconstructing the re- ploitation (Ecur = 0.60; Table 2) was found to be almost cruitment pulses from a time series of length–frequency 90% that gives the maximum relative yield per recruit data (Moreau & Cuende, 1991). (Emax = 0.67) and almost twice than E50, that maintained 50% of the spawning stock biomass (Fig. 5). Recruitment Results shows the bimodal pattern with the minor pulse in re- Descriptive statistics of the sample sizes (n), maximum cruitment during the April–May and major pulse in and minimum values of SL, TL, and W for male, female, September–October (Fig. 6). The minor pulse produced and pooled data, and estimates of the LWR parameters 28.13% and major pulse produced 29.62% recruitment. are presented in Table 1. New maximum total length was recorded for P. khavalchor (17.05 cm) as compared Discussion to previously reported in FishBase (15 cm; Talwar & Uncontrolled exploitation of fishery resources by inland Jhingran, 1991). catch fisheries is considered as the second most notice- The frequency distribution of 427 individuals of differ- able threat to the freshwater fishes inhabiting the ent length class across months (Fig. 1) obtained during Western Ghats of India (Raghavan, Ali, Philip, & Daha- the present study indicated the occurrence of smallest nukar, 2018; Raghavan et al., 2018a; Smith et al., 2011). individuals (55–60 mm) in August and largest individ- However, presently, the gap in the research examining uals (140–145 mm) in January. The FiSAT II output of the impact of biological resource use on freshwater bio- the restructured length frequency data of P. khavalchor diversity or livelihoods is surprising. Fishery manage- population with the superimposed growth curve with ment is a dependent field, and in order to implement the highest ideal fit index (Rn = 0.339) is given in Fig. 2. management plans and conservation actions, concrete The asymptotic length (L∞) was estimated as 149.63 mm data on demography parameters (growth and mortality − and coefficient of growth (K) as 0.71 year 1. The growth rates), status of populations (stock assessments), and parameters estimated using the von Bertalanffy growth number of fish harvested (exploitation levels and rates) model for P. khavalchor and details of the mortality pa- is the primary requirement (Raghavan et al., 2011, 2013, rameters calculated using the length converted catch 2018, 2018a). Nonetheless, such data are readily available curve (Fig. 3) are given in Table 2. Growth performance and confined to a few of the large-growing tropical index (Ø′) was estimated as 4.201. Length at first cap- cyprinids such as the members of the genus Tor (Bhat, ture (Lc) and the maximum possible predicted extreme Nautiyal, & Singh, 2000; Raghavan et al., 2011, 2018a), length for P. khavalchor were found to be 73 mm and with complete absence of information available on other

Table 1 Descriptive statistics, estimated parameters of LWRs (W = a × Lb)forPachypterus khavalchor from Panchaganga River (tributary of Krishna River System) of the northern Western Ghats of India sampled during June 2015 to May 2016 Sex n SL (cm) TL (cm) W (g) LWRs regression parameters Min Max Min Max Min Max a CI of abCI of b Se(b) r2 tp Male 211 5.74 11.62 7.20 14.74 2.43 30.10 0.001 0.001–0.002 3.586 3.476–3.693 0.049 0.961 11.74 < 0.0001 Female 216 6.56 14.22 7.94 17.05* 3.62 46.46 0.004 0.003–0.006 3.183 3.059–3.317 0.058 0.933 3.15 0.0018 Pooled 427 5.74 14.22 7.20 17.05 2.43 46.46 0.003 0.002–0.004 3.336 3.286–3.451 0.038 0.957 9.49 < 0.0001 Italicized values represent significant difference SL standard length, TL total length, W Weight, n number of samples, Min minimum, Max maximum, a intercept, b slope, Se(b) standard error of b, Cl 95% confidence limits, r2 coefficient of determination, t test for isometry, p level of significance *New length record Gosavi et al. The Journal of Basic and Applied Zoology (2019) 80:9 Page 5 of 10

Fig. 1 Contour plot based on length–frequency analysis of Pachypterus khavalchor from the Panchaganga River collected during June 2015 to May 2016, Maharashtra, India groups, including P. khavalchor which is presently cate- contrary, allometric growth can be either positive or gorized as the data-deficient species with possible specu- negative. Positive allometric growth represents that lation of its loss in the near future (Dahanukar, 2011; higher increment in weight as compared to length (fish Dahanukar et al., 2012; IUCN, 2018; Menon, 1999). In becomes stouter or heavier or deeper-bodied). Negative this regard, the detailed investigation of the population allometric growth represents a higher increment in length dynamics of the data-deficient species inhabiting the as compared to weight (fish becomes slender or lighter) Western Ghats of India is the key solution for imposing (Ogunola, Onada, & Falaye, 2018; Wootton, 1998). the conservation action plans. The present study provides Length–weight analysis of pooled (male + female) data the first of its kind information on the population dynam- suggested the fish exhibited significantly higher exponents ics and exploitation levels of the P. khavalchor and em- (b= 3.336) than expected under isometry (b =3),indicat- phasized the instant conservation action for this species. ing the growth of P. khavalchor in the Panchaganga River Fish growth can be measured as either isometric or was positive allometric. According to Beverton and Holt allometric form (Gayanilo & Pauly, 1997; Sarkar et al., (1957), the departure of the ‘b’ value from three is rare in 2013). In isometric growth pattern, both the length and adult fishes. In our case, observed variation in the ‘b’ value weight of the fish increase at the same rate. On the could be attributed to several factors such as length range

Fig. 2 The von Bertalanffy growth curve superimposed over length–frequency data of Pachypterus khavalchor from the Panchaganga River, Maharashtra, India Gosavi et al. The Journal of Basic and Applied Zoology (2019) 80:9 Page 6 of 10

Fig. 4 Length-based virtual population dynamics for Pachypterus khavalchor from the Panchaganga River, Maharashtra, India

(e.g., introduced species), exploitation (e.g., inland fisher- Fig. 3 Length-converted catch curve for Pachypterus khavalchor from the Panchaganga River, Maharshtra, India ies), or conservation of species at risk (Rodríguez-Olarte, Taphorn, & Agudelo-Zamora, 2018). Presently, no information is available from other known localities on the used, season, stomach fullness, gonadal maturity, diet, LWRs parameters of P. khavalchor thus comparative ana- sampling gear, mesh size, fishing pressure, and presence lysis cannot be performed. or absence of disease and parasite (Froese, 2006;Ogunola The earlier study by Prasad et al. (2012) on Yellow et al., 2018). However, these factors were not considered Catfish Horabagrus brachysoma (Günther, 1864), which in the present study, and thus the observed variations in is another member from family Horabagridae showed LWRs parameters could be due to the effect of a single asymptotic length (L∞) and VBGF K value as 422 mm − factor or synergistic effect of multiple factors. Fish with and 0.55 year 1 respectively. In comparison with the re- ideal growth shows the coefficient of determination (r2) sults of Prasad et al. (2012), the P. khavalchor exhibit between 0.90 and < 1 (Hanif, Siddik, Chaklader, Pham, & lower asymptotic length (149.63 mm) and high growth − Kleindienst, 2017). The r2 value in the present study was rate (0.71 year 1). The growth performance index value found to be within expected range (> 0.93) indicates the (ø′) of 4.201 observed in the present study was found to proper fitness of the model for growth and good health be comparatively higher than that obtained for other status of the study species. Length–weight relationships tropical freshwater catfish species including those be- (LWRs) data of the fishes have several applications such longing to the families Schilbeidae (initially P. khaval- as indirect estimation of body weight based on the body chor was classified under the family Schilbeidae and is length, calculation of condition indexes, and also for com- recently classified into family Horabagridae; ø′ be- parisons of species’ growth trajectories (Chen et al., 2018; tween 2.18 and 2.78) (Etim et al., 1999), Claroteidae Froese, 2006; Ogunola et al., 2018). Additionally, LWRs (ø′ = 2.32) (Abowei & Davies, 2009)andSynodontidae are essential tools for the monitoring and conservation of (ø′ = 3.09) (Ofori-danson, Vanderpuye, & De Graaf, fish populations, because they allow us to increase the ef- 2001). High growth rates and growth performance fectiveness of management strategies, whether for control index could be considered as the positive point in

Table 2 Growth, mortality, and exploitation parameters of Pachypterus khavalchor from the Panchaganga River, Maharshtra, India Growth and longevity parameters Mortality and exploitation parameters Asymptotic length (L∞) 149.63 mm Total mortality (Z) 2.23 year−1 VBGF growth constant (K) 0.71 year−1 Natural mortality (M) 0.88 year−1 −1 Minimum length in sample (Lmin) 57.50 mm Fishing mortality (F) 1.35 year

Maximum length in sample (Lmax) 142.5 mm Length at first capture (Lc)73mm

Growth performance index (Ø′) 4.201 Exploitation ratio (Ecur) 0.60

Potential longevity (tmax) 4.22 years Exploitation ratio (Emax) 0.67

Normalization constant (a) of LWR 0.0032 Exploitation ratio (E50) 0.36 Scaling power (b) of LWR 3.33 Z/K ratio 3.14 Gosavi et al. The Journal of Basic and Applied Zoology (2019) 80:9 Page 7 of 10

managers to determine what should be the minimum size of the target species of a fishery (Kolding, Tirasin, & Karenge, 1992; Prasad et al., 2012). Due to the complete absence of the published data on reproductive biology parameters of this species, it is hard to interpret whether the immature individuals are exploited. However, several times extremely small-sized P. khavalchor population was observed (57.50 mm; minimum size in the study population) in the market for selling indicating that P. khavalchor is likely to be fished out before they mature and breed, subsequently contributing to reproductive damage and thus could be reducing the spawning stock of the species. Information on the size at maturity would be useful in re-appraised of mesh-size in this area to prevent cropping of small individuals. Clearly, investigations designed to Fig. 5 Relative yield-per-recruit (Y′/R) and relative biomass-per-recruit understand various reproductive biology parameters of (B′/R) analysis for Pachypterus khavalchor from the Panchaganga this species with special attention on the size at maturity River, Maharashtra, India would be particularly welcome. Based on the virtual population analysis, it is clear that terms of the aquaculture practice for this species (Raghavan juvenile (< 52.5 mm in size) of the P. khavalchor facing et al., 2018a; Williams, Vijayalekshmi, Benziger, Karim, & high natural mortality in the study area. Absence of data Nair, 2016). Additionally, high growth performance index on the natural mortality from other localities restricts value in P. khavalchor is an interesting observation because our intraspecific as well congeneric comparison. How- − as phi prime (ø′) is known to be highly species-specific par- ever, the observed natural mortality (0.88 year 1)inP. ameter with their values being similar within related groups khavalchor was found to be higher as compared to the or taxa (Prasad et al., 2012). Interestingly, it has been shown other catfish species such as Clarotes laticeps (0.87) that the ø′ value remains constant between populations of (Abowei & Davies, 2009), Schilbe intermedius (0.81) thesamespecies(Pauly,1979, 1981;Pauly&Munro,1984). (Etim et al., 1999) and Schilbe mystus (0.28) (Kolding et Lack of data on ø′ across the distribution range of P. al., 1992). Such high natural mortality could be attrib- khavalchor restricts between population comparisons. uted to various factors such as predation, diseases, or The length at first capture (Lc) and maximum possible different environmental stressors acting independently predicted extreme length for P. khavalchor for the popula- or synergistically (Caveriviere & Toure, 1996; Raghavan tion was estimated to be 73 mm and 143.51 mm, respect- et al., 2018a; Richu, Dahanukar, Ali, Ranjeet, & Ragha- ively, indicating that more than 50% of the population is van, 2018). However, the exact information on the being caught before they grow half of their maximum size. factor/s causing higher natural mortality at the small size The Lc not only provides important information regarding of P. khavalchor is not known and thus need further in- the estimated real size of fish in the fishing area that are vestigation. On the contrary, mortality of larger size in- being caught by specific gear, but also enables the fishery dividuals (> 67.5 mm) indicating the greater fishing pressure. According to the Kumbar and Lad (2014) various catfish species inhabiting the Krishna River basin including P. khavalchor is subjected to various threats such as habitat modifications caused by dams, habitat loss due to sand mining, rapid development in urbanization, increasing pollution, overexploitation, destructive fishing methods (dynamite fishing). Higher fishing mortality in P. khavalchor could be attributed to the any of the above mentioned factor/s. According to Gulland (1985), in an optimally exploited stock, fishing mortality should be equal to natural mortality (F = M), resulting in an exploitation rate (E)of0.50. However, according to Patterson (1992) the fishing rate satisfying the optimal exploitation level of 0.5 tended to Fig. 6 Recruitment pattern for Pachypterus khavalchor from the reduce the fish stock abundance and, hence, the former Panchaganga River, Maharashtra, India author suggested that ‘Ecur’ should be maintained at 0.40 Gosavi et al. The Journal of Basic and Applied Zoology (2019) 80:9 Page 8 of 10

for optimal exploitation of those stocks. In the present status by IUCN as per suggestion by Jarić,Courch- study the estimates of the fishing mortality (1.35 year1)for amp, Gessner, and Roberts (2016), so as to increase P. khavalchor is close to twice as compared to natural the focus of the scientific community and conserva- − mortality (0.88 year 1) and exploitation (E) is 0.60 indicat- tion decision-makers on P. khavalchor in order to ing that the study species is being heavily exploited and avoid the risk that necessary conservation measures overfished in the study area. The results are further sup- are implemented too late. ported by the Z/K ratio (3.14), since according to Etim et al. (1999), Z/K ratio ≈ 2 indicate over-exploitation. The Abbreviations B′/R: Relative Biomass per recruit; E: Exploitation; Ecur: Current exploitation current exploitation level (Ecur) was estimated at 0.60 for rate; F: Fishing mortality; FiSAT II: FAO–ICLARM Stock Assessment Tools II; P. khavalchor with predicted E50 and Emax of 0.36 and K: Growth coefficient; L∞: Asymptotic length; LWRs: Length–weight 0.67 respectively. This indicates that the present level of relationships; M: Natural mortality; SL: Standard length; T: Average annual temperature; TL: Total length; tmax: Potential longevity; VBGF: Von Bertalanffy exploitation (Ecur = 0.60) is almost 90% that gives the growth function; VPA: Virtual population analysis; W:Weight;Y′/R: Relative yield maximum level of exploitation (Emax =0.67)andalmost per recruit; Z: Total mortality twice than E50 that maintained 50% of the spawning stock biomass. For continuity of the species in the Acknowledgements The authors sincerely acknowledge the constant support, encouragement study area, it is necessary to maintain at least 50% of and valuable suggestions by Neelesh Dahanukar, Indian Institute of Science the spawning stock and therefore the current level of Education and Research (IISER) Pune, Maharashtra, India. Thanks are also due to the Annapa, Sunny, Nitin Sawant, Swapnil Chaudhary, Siddhesh Rajpure, exploitation need to decrease from 0.60 (Ecur)to0.36 Chandani Verma, Pankaj Gorule and Manoj Pise for their support during the (E50) which is approximately by 44%. Presence of the field work and specimen collection. two bouts based on recruitment patterns indicating that P. khavalchor may exhibit two or extended spawning Funding periods per year. However, a detailed investigation of The research was supported by grants from University Grant Commission (UGC) under minor research project, file number 47-914/14 (WRO) New Delhi various reproductive biology parameters such as and Department of Biotechnology (DBT), Government of India under DBT- gonado-somatic index, size at maturity, sexual di- STAR College Scheme awarded to Modern College of Arts, Science and Com- morphism, spawning season, fecundity and spawning merce, Ganeshkhind, Pune, Maharashtra, India. frequency is suggested. Availability of data and materials Data is available with corresponding author and will be made available on Conclusions and implications for conservation request. It is clear from the present investigation that P. khavalchor population facing the high rate of the ex- Authors’ contributions ploitation and high fishing pressure in the study area SMG and SSK designed the experiment, performed practical work, carried out the data analysis, and wrote the manuscript. PK and SDT contributed to of the Krishna River system hence appears to be un- the animal collection and practical work. All authors read and approved the sustainable. Since currently there are no management final manuscript. plans for P. khavalchor, a chance of loss of this species is more in the near future. The rational exploitation Ethics approval In India, Indian researchers do not require permission to collect animals of this species can be achieved by the implementation unless the locality of collection is in wildlife protected area (The Gazette of of conservation and management plans such as (a) India, REGD. NO. D.L.–33004/99, section 17). Moreover, the present study decreasing the present fishing pressure by 44% of its was carried out in accordance with institutional and national guidelines for handling the experimental animals. current level, (b) size-limit regulation by gradually increasing the fishing gears mesh size, (c) reconsider- Consent for publication ing the design of the fishing methods adopted in the No human subjects are included. No individual person’s data are included. Krishna River to prevent capture of smaller individuals, (d) strict implementation of rules and regula- Competing interests The authors declare that they have no competing interests. tions in order to minimize destructive fishing methods such as dynamite fishing, (e) time-limit regu- ’ lation by restricting the fishing during spawning Publisher sNote Springer Nature remains neutral with regard to jurisdictional claims in period, and (f) declaring a portion of the rivers inhab- published maps and institutional affiliations. ited by P. khavalchor as a natural history reserve (in support to Menon, 1999) to ensure persistence of this Author details 1Department of Zoology, Modern College of Arts, Science and Commerce, fish. Furthermore, due to lack of information across Ganeshkhind, Pune, Maharashtra 411 016, India. 2Post Graduate Research the distribution range, extensive and uncontrolled Centre, Department of Zoology, Modern College of Arts, Science and 3 exploitation, and possibility of being threatened spe- Commerce, Shivajinagar, Pune, Maharashtra 411 005, India. Department of Zoology, Maharashtra College of Arts, Science and Commerce, Mumbai, cies, it is recommended to use the flag of potentially Maharashtra 411 008, India. 4Department of Zoology, Savitribai Phule Pune threatened (PT) species along with data-deficient University, Ganeshkhind, Pune, Maharashtra 411 007, India. Gosavi et al. The Journal of Basic and Applied Zoology (2019) 80:9 Page 9 of 10

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